Method of treating oil and gas wells



, freeze" the drilling producing formation.

Patented Oct. 21, 1941 warren TATES PATENT OFFICE" rmrnoo or rsaaiiiz zi mmesswmss I I FraA.

Calla, I nany, San Delaware 1936, Serial No. 99,943.

cation March 25', 1940,

Bent and Albert G. Loomil, Berkeley, ore to Shell Development Com- Francisco, Calif e corporation of 4 No Drawing. originalapplication September a,

Divided and this appli- SerlalNo.825,833 (01. 252-85) and gas formations without interfering with the.

' oil and gas wells, and is more specifically concerned with a methodjof solidifying unstable formations and selectively sealing off water and gas formations traversed by wells.

This application is a division of our copending application Serial No. 99,943, filed September 9, 1936.

Besides oil-bearing formations, wells usually pass through a variety of formations, such as layers of loose or unstable ground, water-bear-.

ing layers, and gas-bearinglayers.

' It isof great importance to seal ofi or solidify unstable formations, such, for example, 8. ,.heaving shale, since they cause considerabletrouble by caving in, both during drilling, when they tools, and during production, when they. clog the perforated liners and screens, and reduce the fluid flow from the well. Water layers must be sealed ed, as required by law,-to prevent the penetration of water into the oil-bearing formations. Production of water with oil from wells is. moreover, highly undesirtral in character. have able since it causes emulsions and corrosion of the equipment.

Gas'layers must be sealed ofl because an excessive production of gas is often wasteful and leads to a rapid lowering of the reservoir potential.

Furthermore, unless the water and gas layers are sealed off before a well is subjected to an acidizing treatment, the eflect of the acid will be greatest on the water layers, because of the miscibility of acid with water, and on the gas layers,

of the oil layers. As a result of the treatment,

- theundesirable flow of water or gas will there- 'fore beincreased much more than the desired flow of oil. Many methods have been proposed for sealing oil-undesirable formations- Water and gas layers in top or bottom zones, that is, above orbelow the oil-bearing strata can be sealed 0!! by P cementing or by usingformation packeta- However, water and gas layers in'intermediate zones, that is. in zones lying between two or more oilbearing -strata,. cannot be sealed oil. by these methods without shutting'ofl at least one oil- It'isthe object of this invention to provide a chemical method of treatment for stiflening-and solidifying unstable, loose, heaving or caving formationsntraversed by a borehole.

It is also the object of this invention to proyide amethod for selectively sealing'off water wherein albibecause of their porosity, to the detrimentbe formed within a borehole during the drillin thereof.

. The method of the present pounds of silicon, capable of reiict'ing with water to form an insoluble sheath or plug on the walls of the borehole or within the adiacent formations.

For example, organic compounds of silicon can be used to deposit silica and/or more complex silicon compounds, such deposition being effected by hydrolysis and/or condensation of the silicon compounds. The products of hydrolysis or con-- densation of organic silicon compounds are neuno detrimental corrosive effect on the drilling enuipment. and .do not attack chemically the minerals constituting the strata. Limestone strata, in particular, ar left unchanged. In these respects, the organic comorganic compounds, con. The latter compounds form hydrochloric acid on hydrolysis and this acid maycause corrosion of the equipment in the borehole, and

water-bearing formations, particularly when such formations are limestone or contain calcium carbonate. Another advantage oi the organic compounds of silicon is that they are stable and non-volatile, and their use does not offer using the halogen compound of silicon.

The organic compounds of silicon which can be used to carry out the process or this inven- 40 tion may be generally defined as hydroly'sable derivatives of silicone (SiHi'), in which at least one of the hydrogen atoms attached to the sill con atom has been substitutedby an 'alkyl or arylradical, attached to the silicon atom through an 3 oxygen atom. The hydrogen atoms'of silicone l0 Them which have not thusbeen repla'cedby oxy-alkyl or oxy-arylredicals, may further be mbstituted by radicals selected from the group eonsisting oialkyls, aryls, O,'OH. urn, (:1. N01. 88. endsoi.

above can therefore be lowing rormnle: (I)

si (om-1'51 invention. consists of introducing into wells certain, organic compounds of silicon are greatly superior to its in-- such as the halides of silialso will tend to increase the permeability of the the hazard of silicosis which isi incurred when compounds of silicon 'deflned represented by the. fol-J (2) (OR) 3 Si-Si (OR/)3 r RaSl-Si (OR/)3 wherein R andR' may be identical or different alkyl or aryl radicals.

It has been found that very good results are obtained by carrying out the process of this invention with silicon esters, since these compounds hydrolyze readily and their rate of hydrolysis can be accurately controlled. The same is true of condensation products obtained, for example, by combining 2 mols of a silicon ester or esters with 1 mol of water, and eliminating 2 mols of alcohol. These condensation products may be represented by the formulae:

(3) (R0); Si--OSi (OR'):

or R3SiO-Si (OR'):

The condensation of the silicon esters may be also carried out by combining 2' or more mols of an organic ester or esters with elimination of water. The condensation products thus obtained may be represented by the following formulae:

R2n+2SinOan+i (ortho) RuSinOan (meta) Rzn-zsinuan-i (deutero) Ran-4SlnQsn-2 (tritero) Rzn-GSinOIin-Zi (tetrero) Rzn-BSinOBn-4 (pentero) The following specific examples of the organic silicon compounds defined above and suitable for the purposes of this invention may be given:

(1) ethyl ester of tri-methyl silicon,

(CH3) 3Si(OC2Hs) di-ethyl ester of di-ethyl silicon,

' (CaHs) 2Si(OC2Hs)2 tetra ethyl silicate, Si(OC2H5)4 tetra phenyl silicate, SMOCsHs) 4 di-ethyl ester of di-phenyl silicon,

(CeI-IahSNOCzHsM di-ethyl silicon oxide, (C2Hs)2SiO tri-ethyl silicol, (CzHs) 3SiOI-I di-phenyl silicol, (CaHs) 251(011) 2 silico-propionic acid, (Cal-Is) SiO(0I-I) silico-benzoic acid, (CsHs) SiO(0H) tri-ethyl chloride of silicic acid, SiCl (OCzHs) tri-ethyl amide of sllicic acid,

Sl(NH2) (OCzI-Is) 3 acid,

Si (NH2) (OCHa) s tri-ethyl nitrite of silicic acid,

- SKNOz) (002115) tetra-p-aminoethyl--orthosilicic acid ester,

Si (002mm) 4 hexa-methyl ester of (ii-silicon,

' (CHsO) 351-51 (0330) a tri-methyl-tri-phenyl ester of di-sillcon,

'(CHaO) aSi-Si (CsHsO) a tri-methyl-tri-phenyl disilicate,

(CI-I30) aSi-O-Si(OCsH5) a hexa-ethyl disilicate.

' (CaHoO) aSi-O-SHOC'aHs) a methyl-ortho-tri-silicate (CHa)aSlaO1o ethyl-meta-tetra-silicate (C2H5) aShOu methyl-tetrero-penta-silicate (CH3) 4815012 tri-methyl amide or silicic The method of introducing these materials into the. wells depends upon the particular conditions encountered and the particular objective sought.

If the process of this invention is applied during the drilling of a well for the purpose of solidlfying unstable formations and forming a mud sheath of particular strength on the walls of the borehole to prevent the escape of gases, the infiltration of water into the well or a loss of the circulation fluid into porous formations, a nonaqueous solvent consisting of or comprising any desired organic silicon compound may be used to form the drilling fluid in combination with materials such as clay, shale, limestone, and/or, if desired, suitably ground weighting materials such as barytes, galena, iron or lead oxides, etc. The use of such non-aqueous mud fluids is especially effective in preventing difliculties with heaving and caving formations. these non-aqueous suspensions of clay arid/or other solid substances may be peptized or deflocculated, and their viscosity kept at a desirably low value, through the use of suitable stabilizing agents. The best results are usually obtained with stabilizers having a molecular weight not greatly exceeding that of the suspension medium.

7 The following stabilizers may be advantageously used: fatty acids, such as oleic, stearic, palmitic,

naphthenic, etc.; oil-soluble soaps prepared from these fatty acids, for example, calcium, magnesium or aluminum oleates, stearates, palmitates, naphthenates; amines, for example, primary, secondary and tertiary alkylamines such as cetylbe given:

(1) 25 parts of clay are dispersed in 74 parts of a 5% solution of a silicon ester dissolved in alcohol, to which 1 part of pyridine is added, giving a mud fluid of satisfactory viscosity and stability.

(2) 25 parts of clay are dispersed in '73 parts of a 5% solution of a silicon ester dissolved in alcohol, to which 2 parts of sodium stearate soap are added, giving a dispersion satisfactory for drilling purposes and weighing about 10 lbs. per gallon.

Since water or at least small amounts of moisture are found in all strata ordinarily penetrated by a well, a firming, solidifying and cementing chemical, such as silicic acid, will be formed by hydrolysisin the interstices of the formation ad ,iacent the well bore continuously as the bore is It has been found that sunk, water horizons being plugged at the same time, and gas formations being sealed off by the impervious mud sheath formed on the walls of the borehole and supported by the hydrostatic effect of the mud fluid column. Since, therefore, it is not necessary to use any casing or liner until the oil horizon is reached, considerable saving in the cost of drilling wells is effected by the application of the present method.

If a treatment according to this invention applied to a producing well having the usual casing and tubing, the following procedure may be followed if it is desired to seal off a water formation.

The well is preferably first filled with oil, and

' a desired amount of a non-aqueous solution consisting of or comprising anorganic silicon compound is then introduced into the well through the tubing, and is forced into the water and oil horizons by pumping another charge of oil downthe tubing or by applying pressure to the well in any other manner. The solution will diffuse into the formation water, giving by hydrolysis the desired water and. acid-insoluble precipitate of silica. When the flow of the well is reversed.- by pumping or swabbing, that part of the solution which entered the oil horizon is flushed out unchanged, no-hydrolysistaking place in the abs'ence of water, while the'water horizon is effectively plugged. If desired, the well may now be subjected to acid treatment. The acid will not be able to enter the water horizon, and its efiect will be confined to the oil horizon.

In using the method of this invention to seal off gas-bearing layers or for consolidating heav-v ing or unstable formations, the same procedure as for water layers may be followed. If the gasbearing or unstable formations are sufficiently wet, as is often the case, the procedure is similar to that'described above. If the formations are dry, or substantially dry, an aqueous liquid such aswater or brine, maybe introduced into the well and forced into the formations before or t after the injection of the treating solution. Hy-

drolysis of the silicon compound in the pores of materials, so that only the gas-bearing forma- 4 tion is sealed off by the hydrolysis products of the the formations then takes places as describedabove. In order to insure-the formation of the insoluble precipitate as far back within the formation as possible, it may sometimes be desirable to introduce into the well and force into the formation a charge of'a neutral material, such as oil, between the charges of the treating solution and the aqueous liquid.

In treating gas-bearing formations adjacent to oil-bearing formations, and especially in-cases where the present process is to be followed by an acidizing treatment,'a somewhat different procedure may be followed. The tubing and the casing'are first. filled with oil. some pluggin material, such as calcium or iron carbonate slurry, calcium carbonate mud, etc., is now pumped down the tubin to shut oil the oil formation. ithls plugging material being soluble in acid. The oil formation is thus sealed off by a temporary plug or sheath, care being taken not to allow the plugging material to'reach and seal' The well is then treated to the gas formation. I seal off the gas formation according to the process of the present invention, that is, by forcing a charge comprising an organic silicon compound followed by a the gaze-bearing ever, enter. only the gas vented from penetrating charge of an aqueous liquid into formation- These charges, howinto the oil formation formation. being precon compound with a suitable organic organic silicon compounds formed within said formation. The temporary plug or sheath seal-- 'ing oil the oil-bearing formation may subsequently be easily removed by acid treatment or simply by reversing the flow of the well (apressure differential of from five to ten pounds being usually sufficient to remove such sheaths) while the gas formation remains sealed off by the acidinsoluble compounds of silicon formed therein.

This chemical seal in the gas formation may sub- 7 sequently be removed to any desired degree, by

- dissolving it 'with caustic alkali or any other suitable agent while the silicic acid is still in the gel l or hydrated form.

In treating oil wells by any of the methods described above, it is highly desirable to control accurately the rate of hydrolysis of the organic silicon compounds used, since a delayed hydrolysis will result in the precipitation of silica well back in the formation and secure the optimum sealing effect. The rate of hydrolysis may be effectively controlled in the present process in several ways:

(1) By controlling the hydrogen ion concentration (pH) of the treating solution. This may be done either by using small amounts of a catalyst of an acid or basic type, or by changing the constitution of the organic silicon compounds.

namely, by using organic compounds substituted with such groups as, for example, Cl, N02, S02, NHz, etc. The presence of these groups in the silicon compounds-molecules results, upon bydrolysis, in the formation, in addition to silica, of

acidic or basic materials such as nitric acid, sulfuric acid, hydrochloric acid, hydroxyamines, etc., which are formed in amounts sufliciently small toavoid an attack on the formation, but effective in keeping the-pH of the solution at a desired value.

(2) By selecting in each particular case a siliin its molecule, since compounds wit: organic groups of higher molecular weight hydrolyze more slowly.

. (3) In cases where the silicon compounds are I used for treating wells in a non-aqueous solution,

by controlling their concentration in the solvent.

The organic silicon compoundsused for the present process may be prepared by methods well in this known to the art. Reference is made regard to the following publications: Ann. 474, 2'76, 1929 Ann. 57, 331, 1846 Mellor-Comprehensive Treatise, the article'be- S ginning on page 969, vol. 6.

Although the process of described with regard to its uses in well drilling by the impervious plug or sheath formed by the 7s practice, it is obvious that it can equally well be previous treatment with acid-soluble plugging oup (R) this invention-has been applied for sealing ofi, rendering impervious to fluids, or solidifying ground strata which do not lie in the proximity of wells. Thus, the present invention has many practical applications, for example, in building canals, sluices or dykes in porous soil, where it is desirable to stop the percolation of water through the sand, or in constructing bridge pillars, landing piers, tunnels, etc., in ground formations which are not sumciently firm or impervious.

We claim as our invention:

1. In a process for sealing off formations traversed by a well, drilling said well with an inert non-aqueous drilling fluid comprising dispersed clay and a. solution of an ester of silicon in alcohol.

2. In a process for sealing off formations traversed by a well, using a drilling fluid comprising clay dispersed in an inert non-aqueous liquid and a solution of an ester of silicon in an alcohol whereby a mud sheath is formed on the walls of the borehole during drilling, and the strength and fluid-imperviousness of said sheath is improved by the hydrolysis products of the ester of silicon formed upon contact with the water present in the formation.

3. In a process for sealing ofi formations traversed by a well, drilling said well with a non= aqueous drilling fluid comprising dispersed clay and an ester of silicon dissolved in said fluid,

said fluid being incapable of hydrolyzing said ester of silicon.

4. A water-free drilling fluid comprising a non-aqueous suspending liquid, a solid suspended material, and an ester of silicon, said liquid being incapable of hydrolyzing said ester of silicon. ...1T.'I

5. A water-free drilling fluid comprising a non-aqueous suspending liquid, clay, and an ester of silicon, said liquid being incapable of hydrolyzing said ester of silicon.

6. In a process for sealing off formations traversed by a well, drilling said well with a drilling fluid. having a non-aqueous liquid component incapable of hydrolyzing esters of silicon, said drilling fluid having an ester of silicon added thereto.

7. In a process for sealing oif formations traversed by a well, drilling said well with a drilling fluid 'having mineral oil as the liquid component, said drilling fluid having an ester of silicon added thereto.

8. In a process for sealing off formations traversed by a well, drilling said well with a drilling fluid having a non-aqueous liquid component incapable of hydrolyzing esters of silicon, said drilling fluid having an ester of silicon and a peptizing agent added thereto.

FRANK-IN A. BENT. ALBERT G. LOOMIS. 

